Spectroscopic techniques for PFAS detection in soil: A forward-looking review on potentials, limitations, and future directions.

Per- and polyfluoroalkyl substances (PFAS) are highly persistent contaminants widely used in industrial processes and consumer products. Soil is an important PFAS reservoir and a key medium linking contaminant transport, ecological exposure, and human health risks, making effective monitoring essential. Conventional methods, such as liquid chromatography-tandem mass spectrometry (LC-MS/MS), provide high sensitivity and accuracy but require extensive sample preparation, specialised instrumentation, and laboratory infrastructure, limiting large-scale screening and in situ monitoring. Spectroscopic techniques offer rapid, non-destructive, and relatively low-cost alternatives and have been widely applied to soil characterisation. However, evidence supporting spectroscopic detection or assessment of PFAS in soils remains extremely limited. This review critically evaluates existing soil PFAS monitoring methods and relevant spectroscopic studies from a forward-looking perspective. Studies in water and other environmental matrices are considered supplementary evidence rather than direct validation for soils. Particular emphasis is placed on an infrared spectroscopy-based proxy framework using spectrally responsive soil properties associated with PFAS sorption, transport, and partitioning to indirectly assess PFAS behaviour and potential risks. Overall, this review identifies key knowledge gaps and proposes a proxy-based paradigm for rapid screening, risk classification, and spatial assessment of PFAS in soils.